Application Performance and Flexibility on Exokernel Systems

From: Chuck Reeves (creeves_at_windows.microsoft.com)
Date: Wed Jan 21 2004 - 10:34:59 PST

  • Next message: Richard Jackson: "Review: Kaashoek, et al. Application Performance and Flexibility on Exokernel Systems."

    The paper, "Application Performance and Flexibility on Exokernel
    Systems" was submitted to SOSP in 1997 and was written by a number of
    researchers and MIT. It describes their experiences in building and
    testing a number of exokernel operating systems.The exokernel design
    proposes to expose a higher level of control and more information
    relative to hardware and software resources to untrusted software. In
    this model, management of these resources is available to user
    applications, but protection is still guaranteed by privileged software
    running in the kernel. In the designs presented here, the additional
    facilities are leveraged by constructing unprivileged library operating
    systems. Through the use of the additional information exposed by the
    kernel, these libraries are able to provide better, more appropriate
    abstractions for managing frequently-used, expensive resources. Most of
    the examples, revolve around improvements recognized in managing disk
    I/O.

    Section 4 of the document describes the design of a disk management
    system called XN. It's use of UDF's (untrusted deterministic functions)
    as a common abstraction for manipulating ownership and access control
    seemed to enable flexibility in the layout information on disk. The
    authors also discuss some of the details of a file system called C-FFS
    that they built on top of XN.

    Section 5 details Xok and ExOS, an exokernel and it's associated default
    library. I found the idea of providing per-page transformations to
    compress or digitally sign information at an application level an
    interesting indicator of the level of control this approach enables.

    Much of the rest of the document is committed to comparisons of
    measurements taken on the performance of applications running on top of
    Xok/ExOS to those on commercial UNIX offerings. The results do seem to
    confirm that in disk intensive applications, a finer level control can
    result in improved performance.

     


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